The present invention relates to an information reading device which is applied to image forming devices such as thermal ink-transfer color copying machines.
Recently, thermal ink-transfer color copying machines which perform color copying using, for example, thermal ink-transfer ribbon of a plurality of colors have been developed. These color copying machines are generally constructed to comprise an information reading device to read an original and an image forming device which transfers and forms the image information read out by the information reading device on a sheet of paper. That is, the information reading device reads the image information of the original as optical color signals by optically scanning the original which has been placed on an original table, and sends the image information thus read to the image forming device. The image forming device receives the image information from the information reading device, converts it to color information corresponding to each of the colored inks on the thermal ink-transfer ribbon, selects an ink portion of the thermal ink-transfer ribbon corresonding to this color information, and thermally transfers the ink in the selected ink portion to the sheet of paper by means of a thermal head, thus color copying the original by the transfer of the respective colored inks, one after another, onto the sheet of paper.
Conventional information reading devices used for color copying machines are typically constructed in a manner represented in FIGS. 1 and 2. On the top surface of a main body 1, an original table 2 is provided for placing and holding an original (FIG. 2). Below original table 2, a scanner 3 is disposed which optically scans the original on original table 2 by reciprocatively moving in parallel to and along the bottom surface of table 2 in the direction of the arrow A shown in FIG. 1. As shown in FIG. 2, scanner 3 comprises a pair of fluorescent lamps 4, which irradiate the original on the original table 2 with light; a pair of rod lens arrays 5, which lead the reflected light from the portion of the original located between the fluorescent lamps 4; and a charge-coupled device (CCD) image sensor unit 6 which receives the light led by rod lens arrays 5 and converts the light to electrical signals. Each of these units are individually supported by a carriage 7. At the side of carriage 7, a container box 8 is mounted integrally with carriage 7. Inside of container box 8, three printed circuit boards 9 are vertically mounted which include an amplifying circuit to amplify the signal from CCD image sensor unit 6 and an A/D conversion circuit which converts the amplified signals to digital signals. The signals outputted from printed circuit boards 9 are transferred to a central processing unit (CPU) board 11 provided at the bottom of main body 1 through a flat cable 10 (FIG. 1) from which they are forwarded to external circuits.
One end of carriage 7 is slidably fitted to a guide shaft 12 disposed in the longitudinal direction of main body 1 and, at carriage 7, a wheel (not shown in the figure) is rotatably installed and is designed to travel a guide rail (not shown) arranged in parallel with guide shaft 12. A drive pulley 13 is disposed at one end of the guide shaft 12 (rear side of main body 1), and a drive pulley 14 is disposed at the other end (front side of main body 1). A timing belt 15 is extended around pulleys 13 and 14, with one point of timing belt 15 fixed to carriage 7. Drive pulley 13 is driven by a reversibly-rotatably pulse motor 16 installed in the rear portion of main body 1 and scanner 3 is reciprocally movable along and parallel to the bottom face of original table 2 in the direction of arrow A in FIG. 1 (longitudinal direction of main body 1). Near pulse motor 16, at the rear portion of main body 1, a power supply unit 17 incorporated with an inverter circuit to convert DC power to AC power is provided to supply required AC power to fluorescent lamps 4 through a flat cable 18.
The conventional information reading device as described above, however, has the following drawbacks. CCD image sensor unit 6 is constructed by incorporating a CCD line sensor (hereinafter called a CCD sensor) as a sensor element, and various circuits such as CCD sensor driving circuit, a driving power supply line, and an output signal line, on a single ceramic base board. In other words, from the view point of the accuracy requirement for mounting position and height, the CCD sensor is mounted on a very flat ceramic base board having little response to temperature variation, and, in addition, the other circuits (the driving circuit, the driving power supply line, the signal output line, etc.) are also arranged on the same ceramic base board. For the above reason, the width of the ceramic base board, which corresponds to the width of CCD image sensor unit 6, must be about 63 mm. With this construction, however, when the specification or arrangement is changed, the whole ceramic base board must be rebuilt. Furthermore, this causes a problem of producing a warp in the large ceramic base board by as much as or more than 60 mm during manufacturing. Moreover, because of the required high-speed signal transference in the driving circuit, heat is likely to be produced therein, resulting in the CCD sensor experiencing undesirable thermal noise due to the heat.